C# String.GetExtension doesn't return empty string

[doctornoodlearms]

Tested versions

Found in version 4.4.1
Reproducible in version 4.2.2 and 4.5 beta 1

System information

Windows 11 - Godot Engine v4.4.1.stable.mono.official - Intel Core i7 14th Gen - Nvidia Geforce RTX 3050

Issue description

When calling GetExtension() on a string in a C# script if the string doesn't have an extension the full string will be returned instead of an empty string. When called on a string with no file extension at the end an empty string should be returned instead.

Steps to reproduce

1. Create a new C# project
2. Create a C# script
3. Add a string variable with no file extension
4. Call GetExtension() on the string

using Godot;
using System;

public partial class new_script : Node {

	public override void _Ready() {

		// Returns jpg
		string test1 = "test.jpg";
		GD.Print("test 1 ", test1.GetExtension());

		// Returns test
		string test2 = "test";
		GD.Print("test 2 ", test2.GetExtension());
	}
}

extends Node

func _ready():
	# Returns jpg
	var test1 = "test.jpg"
	print("test 1 ", test1.get_extension())

	# Returns empty string
	var test2 = "test"
	print("test 2 ", test2.get_extension())

Minimal reproduction project (MRP)

N/A